This filter was found in an American publication from the 1980s. The circuit can be implemented with any operational amplifier. The power supply must be symmetrical.
This circuit is from a 1995 technical documentation. The transistor can be a BC558 and the sensor...
Found in a Popular Electronics from the 90s, this circuit checks the presence of voltage on a...
The critical component of this amplifier is the output transformer. We found the circuit in an old...